Kidney Disease in Cats: Symptoms, Stages, and Management

Kidney disease in cats, usually chronic kidney disease, is a gradual, irreversible loss of kidney function that is one of the most common conditions of older cats. The kidneys filter waste, balance water and minerals, and help control blood pressure; as their working tissue is lost, waste builds up in the blood and the body struggles to hold on to water. It develops slowly, so a cat can lose a large share of kidney function before looking unwell at all.

This is why our cat health guide keeps returning to the same theme: in cats, the first job is noticing small changes. Kidney disease is the condition where that skill pays off most.

What kidney disease in cats is

Chronic kidney disease (CKD) is the long-term, progressive loss of the kidneys’ filtering units, which the body cannot replace. It is one of the leading causes of illness in senior and geriatric cats, and the risk rises steadily with age; the kidneys have a lot of spare capacity, so signs typically appear only once roughly two thirds of function has been lost. A separate condition, acute kidney injury, comes on suddenly (for example after a cat eats a lily or licks antifreeze) and is an emergency rather than the slow disease most owners mean.

When my own cat Biscuit started leaving heavier, wetter clumps in the litter tray at about twelve, I genuinely thought I was imagining it. I wasn’t: that small change was the first sign, and I’m glad I mentioned it rather than waiting.

Symptoms of kidney disease in cats

The hallmark early signs are increased thirst and increased urination, often the very first thing an owner notices. As the kidneys lose the ability to concentrate urine, cats pass more water and drink more to keep up. Over weeks to months you may also see:

• Gradual weight loss, often with muscle wasting along the back
• A reduced or fussy appetite, sometimes with nausea or drooling
• A duller, more unkempt coat and lower energy
• Vomiting, and bad breath that can smell faintly chemical
• Mouth ulcers in more advanced cases

Because these creep in slowly and cats are experts at masking illness (see our guide to the signs your cat is sick), they are easy to dismiss as “just getting old”. In an older cat, increased drinking is never just old age until a vet has ruled out kidney disease, diabetes, and an overactive thyroid.

How vets diagnose and stage it

Vets confirm kidney disease with blood and urine tests, then assign a stage that guides treatment. Blood tests look at waste products: urea, creatinine, and SDMA, a marker that can flag the disease earlier, sometimes when only about 40 percent of function is lost rather than the roughly 75 percent at which creatinine reliably rises. A urine test shows how well the kidneys still concentrate urine, and a protein measurement and blood-pressure reading complete the picture.

The international standard is the IRIS system (the International Renal Interest Society), which sorts cats into four stages, from stage 1 (very early, minimal signs) to stage 4 (advanced, with marked waste build-up). Around 1 in 5 cats with chronic kidney disease also develop high blood pressure, which can quietly damage the eyes, brain, and heart, so blood pressure is part of every full work-up. The stage decides how aggressively the disease is treated and how often your cat is rechecked.

How kidney disease in cats is managed

There is no cure, so management aims to slow progression and keep your cat feeling well. The single most evidence-based step is a therapeutic renal diet: a complete food with controlled phosphate and high-quality, moderated protein, which studies link to longer survival and fewer “crisis” episodes. The main pillars of care are:

• Diet: a vet-prescribed renal food, introduced gradually over about 7 days. Our guide to feeding a cat with kidney disease covers how to make the switch when a cat is fussy.
• Hydration: more water lightens the kidneys’ load. Wet food, water fountains, and several bowls all help; see how to get a cat to drink more water.
• Phosphate and blood pressure: phosphate binders and blood-pressure medication are added when tests show they are needed.
• Comfort and complications: anti-nausea medicine, appetite support, and treatment for anaemia, which affects a meaningful minority of cats in later stages.

Most of this happens at home, with rechecks (typically every 3 to 6 months, more often in later stages) to adjust the plan.

Living with a cat who has kidney disease

A diagnosis is not the end of a good life; many cats live comfortably for months to years with steady management. Because chronic kidney disease overlaps so much with simply growing older, it sits at the heart of our senior cat care guide, and the twice-yearly senior check (every 6 months rather than annually) is what catches it early. Keep the routine boring and consistent: the prescribed food, easy access to water, quiet feeding spots, and a note of anything that changes.

With Biscuit, the thing that kept me sane was a simple weekly weigh-in on the kitchen scales and a tally of how much water went into the fountain. Numbers told me how she was doing on the weeks she was too dignified to.

This guide is general information, not a diagnosis. If your cat is drinking more, losing weight, or just seems “off”, please have your own vet examine them, since they can run the tests and know your cat’s history.